How to Incorporate Step-Wise Potential into Schrödinger Equation for a 1D Box?

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Homework Help Overview

The discussion revolves around incorporating a step-wise potential into the Schrödinger equation for a one-dimensional box. The potential is defined as V(x) = -Vo exp(-x/L) for 0 < x ≤ L and V(x) = ∞ for x ≤ 0. Participants are exploring how to set up the equation given these boundary conditions.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to formulate the time-independent Schrödinger equation (TISE) with the given potential and are questioning how to incorporate the step-wise nature of V(x) into the equation. There are inquiries about the behavior of the wave function in regions outside the defined boundaries, particularly for x < 0 and x > L.

Discussion Status

Some participants have suggested solving the Schrödinger equation in each region and matching the solutions at the boundaries. There is ongoing clarification about the implications of the potential outside the specified range and the necessity of boundary conditions.

Contextual Notes

Participants note that the conditions for x < 0 and x > L are not explicitly defined, leading to questions about their relevance in the context of the problem. There is also mention of needing to use the TISE to derive a general form of the wave function and solve for constants based on boundary conditions.

Litmus
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Homework Statement



Trying to construct Shrodinger Equation given:
* mass: m

* Boundary Conditions: (potential)
V(x)=-Vo exp(-x/L) for 0<x≤L
V(x)=∞ for x≤0

Homework Equations



The Attempt at a Solution



(-h^2 / 2m ) (d^2 ψ / dx^2) + V(x)ψ = E * psi

Not sure how to incorporate step-wise V(x) into above eq.
 
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Hi Litmus, welcome to PF!

Litmus said:
* Boundary Conditions: (potential)
V(x)=-Vo exp(-x/L) for 0<x≤L
V(x)=∞ for x≤0
What about ##x> L##?

And what can you say about the wave function for ##x < 0##?
 
You need to solve the Schrödinger equation in each region and then match the solutions at the boundaries. Your book should have examples of how to do this.
 
What about x>L?

And what can you say about the wave function for x<0?

I don't understand. I've given conditions x<0, and x>L it's not specified. Why do we care?

vela said:
You need to solve the Schrödinger equation in each region and then match the solutions at the boundaries. Your book should have examples of how to do this.

Like this?
(-h^2 / 2m ) (d^2 ψ / dx^2) + [-Vo exp(-x/L) ] ψ = E * psi
(-h^2 / 2m ) (d^2 ψ / dx^2) + ∞ψ = E * psi

Boundary is 0 so:
(-h^2 / 2m ) (d^2 ψ / dx^2) + [-Vo] ψ = E * psi

... how do I proceed?
 
Litmus said:
I don't understand. I've given conditions x<0, and x>L it's not specified. Why do we care?



Like this?
(-h^2 / 2m ) (d^2 ψ / dx^2) + [-Vo exp(-x/L) ] ψ = E * psi
(-h^2 / 2m ) (d^2 ψ / dx^2) + ∞ψ = E * psi

Boundary is 0 so:
(-h^2 / 2m ) (d^2 ψ / dx^2) + [-Vo] ψ = E * psi

... how do I proceed?

The problem can be tackled in the following steps:

1. Use TISE to get a general form of the wavefunction
2. Solve for the constants in the general wavefunction using boundary conditions
 

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